Katsav, 66, left Ma'asiyahu Prison in Ramle for the first time since beginning his sentence in December, in order to attend the wedding of his son Noam.
The former president is currently serving a seven-year prison sentence after being unanimously convicted in the Tel Aviv District Court in 2010 of two counts of rape, two counts of sexual harassment, an indecent act using force and obstruction of justice.
Under the terms of his release, Katsav was not allowed to visit his home in Kiryat Malachi, and was barred from giving interviews to the press. He was free to mingle with the wedding guests, the Jerusalem Post reported.
The former president must return to the prison by midnight today.
The Supreme Court ruled last week that Katsav would not be allowed a further appeal hearing in his rape trial.